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Electrical responses of isolated nitella protoplasm — Excitations or artifacts?

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Summary

Isolated protoplasmic droplets of the alga Nifella were investigated with microelectrodes under current clamp conditions. The following observations were made:

  1. 1.

    Long pulses of either polarity yielded almost symmetric current-voltage relations. Near the rather small resting potential (inside negative) the measuring points lay on a straight line corresponding to an apparent surface membrane resistance of 1.7±0.45 kΩ (mean ± S.E.M.,n=5).

  2. 2.

    Experiments with various pulse programs revealed no mechanism comparable to Na inactivation but stressed the electrical symmetry of the droplet with respect to the resting potential.

  3. 3.

    Changes of the [Ca2+] in the bathing medium between 0 and 10 mM as well as of the pH between 5 and 9 did not influence the responses. Replacing K+ by Na+ (or vice versa) or exchanging NO 3 for acetylglycine or Cl was also ineffective.

These observations are not consistent with a normal excitable surface membrane. Similar responses are obtained with a RC network which is described and which may have its substrate in histological peculiarities of the protoplasmic droplet.

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References

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Koppenhöfer, E. Electrical responses of isolated nitella protoplasm — Excitations or artifacts?. Pflugers Arch. 361, 263–267 (1976). https://doi.org/10.1007/BF00587291

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Key words

  • Isolated protoplasm
  • Nitella
  • Electrical responses
  • RC network